In order to enable stable reading and writing operations, substrate materials for conventional optical discs must contain minimal quantities of foreign substances or impurities, exhibit a high level of transparency, a small birefringence, a low level of moisture absorption to prevent deformation of the optical disc, and excellent heat resistance, and must also exhibit favorable fluidity and excellent releasability to ensure favorable molding characteristics, and consequently polycarbonates and epoxy resins and the like are widely used (for example, see Patent Document 1).
Polycarbonates and epoxy resins can be heat molded, and may also be used to form an optical disc substrate by laminating two layers together. Although optical discs with this type of substrate exhibit excellent strength, attempts to destroy such discs by physical force at the time of disposal in order to protect the information contained thereon either result in failure to destroy the disc, or even if destruction is successful, generate sharp fragments which must be handled with care. Furthermore, even if attempts are made to separate and recover the materials such as metals used in the reflective layer and the recording layer, to enable these materials to be reused, separating the various materials is impossible, making recycling extremely difficult.
Another problem that arises with conventional optical discs is that although printing methods, such as silk screen printing, are the most commonly used when lettering or images are printed on the surface of the disc, silk screen printing is unable to generate finely detailed images.
Furthermore, with silk screen printing, in order to enable different lettering or images to be printed on each disc, as in the case of serial numbers, the printing plate must be changed on each occasion, so that in the case of conventional optical discs, the printing of variable information onto each disc is not feasible from a practical viewpoint.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H05-258349